SQL CHECK Constraint

SQL CHECK Constraint:

The CHECK constraint is used to limit the value range that can be placed in a column.

If you define a CHECK constraint on a column it will allow only certain values for this column

SQL CHECK on CREATE TABLE:

CREATE TABLE Persons (ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
CHECK (Age>=18)
);

CHECK constraint on multiple columns:

CREATE TABLE Persons (ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
City varchar(255),
CONSTRAINT CHK_Person CHECK (Age>=18 AND City='Sandnes')
);

SQL CHECK on ALTER TABLE:

ALTER TABLE Persons ADD CHECK (Age>=18);